In relation to some diseases patients must inject a medicament on a regular basis such as once weekly, once daily or even a plurality of times each day. In order to help patients overcome fear of needles, injection devices have been developed that involves auto-insertion of the needle which makes operation of an injection device as simple as possible. Such devices are typically designed as auto-injectors which provide automatic expelling of the medicament. In order to perform an injection, the user shall position the injection device onto the injection site and activate the device. Such activation causes the device to insert a needle into the skin, eject a dose of the medicament and subsequently move the needle into a shielded position.
For injection devices that use a cartridge without integrated injection needle, it is a requirement that the medicament container is connected to an injection needle in order for the medicament to be injected into the patient. The needle however must not be mounted prior to use as this will compromise the sterility of the needle and cartridge and could lead to contamination of both. The needle must therefore be mounted just before the device is used.
The procedure of mounting an injection needle to the device involves extensive handling of the needle which can result in unintentional needle cuts, contamination or damaging of the needle. Furthermore the needle handling can lead to users finding the device more difficult to use.
Designing the device to incorporate the needle will remove needle handling, however existing needles are difficult to use as internal needles, due to the design of their device interface, which typically requires a turning motion for mounting and their packaging comprising a needle container and a sterile barrier which under normal use are removed manually prior to mounting.
One example of an auto-injector incorporating an injection needle that is kept separate from the cartridge prior to use and which addresses the sterility issue is disclosed in WO 01/07104. In this reference, the needle assembly comprises two separate resilient needle sheaths for respectively protecting the front and rear needle. Typically, this type of needle sheath is made from latex rubber. During use, the needle sheaths are penetrated by the respective needle sections. Although ensuring sterility before use, the needle assemblies incorporating flexible needle sheaths typically leads to an increase in expenses during manufacture. In addition, mechanical impact during manufacture or during handling may lead to the sheaths becoming prematurely penetrated thereby compromising sterility of the injection needle.
U.S. Pat. No. 5,829,589 discloses a pen needle magazine dispenser to be received in a cap of a medication delivery pen. A plurality of cavities are formed in the dispenser. Each cavity accommodates a pen needle assembly. A disc shaped label or sterility barrier provides sterility for unused pen needle assemblies. Although the label is claimed to offer controlled breaking when an adaptor equipped delivery pen is pressed through the label the manual handling of the pen and the magazine dispenser does not provide for a user-friendly operation.
In a further reference, US2003/0144633 two example designs of a needle assembly are shown that involves a rear needle section of the injection needle that is kept in a sterile chamber by means of a film-type seal attached to the walls forming the chamber. The needle assembly is incorporated in an auto-injection device wherein a pre-stressed spring is used to drive forward a container and subsequently drive forward a piston of the container during the expelling operation. Upon triggering of the device, the container is driven forward so that the container penetrates through the film seal into the sterile chamber. This causes connection between container and the rear portion of the injection needle. The needle assemblies involve additional openings which necessitates use of further sealing members. Further, the particular designs of the disclosed needle assemblies are not particularly well-suited for use in connection with standard type injection devices, such as multi-use pen injectors where the needle handling is performed manually. This makes the manufacturing of the disclosed needle assemblies particular expensive. In addition, by using the one and same spring for facilitating both the penetration of the film-type seal as well as for injecting the medicament, an optimized operation of the two parts of the operation is very difficult to achieve.
Having regard to the above-identified prior art devices, it is an object of the present invention to provide an injection device incorporating a standard needle assembly of the conventional type used for multi-use pen injectors and which facilitates improved and consistent unsealing of the sealing member of the needle assembly.
Yet additional further objects of the invention are to provide measures for obtaining devices having a superior performance, providing easy operation and, at the same time, enabling manufacture at a reduced cost.